The spatial distribution of gap junctions between myocytes is a key determinant of electromechanical function in the developing and mature heart. Breakdown of the normal geometry of gap junctional connectivity in diseased hearts may give rise to substrates for re-entry, arryhthmia and conduction disturbance. Based on published and preliminary findings, we hypothesize that the patterning and maintenance of myocardial gap junction distribution is determined by the 3D disposition of intercellular adhesive contact between myocytes. Specifically, during postnatal differentiation of working myocardial tissues, there is a preferential turnover and/or selective vulnerability to loss of gap junctions not associated with cell adhesion junctions (ie, adherens junctions and desmosomes). We propose that this gives rise to non-uniformities in the pattern of intercellular electrical contact, critical to differentiation of anisotropy, discontinuity and other electrophysiological characteristics important to the normal function of adult cardiac muscle. To evaluate this hypothesis, we propose to; a) characterize spatiotemporal patterns of association between gap junctions and cell adhesion junctions during postnatal growth of ventricular myocardium, and examine the assembly and degradation of intercellular junctions over a similar time course; b) do correlative studies of postnatal changes to gap junction distribution and action potential (AP) conduction patterns (assessed by potentiometric dye and optical mapping of activation), in living myocardial preparations; c) use cultures of aligned myocytes to investigate remodeling of intercellular electromechanical contacts in vitro and correlate these changes to alterations in AP conduction properties assessed from optical maps of activation; d) use retroviral constructs (expression dominant negative N-cadherin or desmocollin molecules to determine whether targeted disruption of adherens and desmosomal junctions; (I) alters gap junction distribution and (ii) influences conduction properties in aligned myocyte cultures; and e) determine, using these same viral constructs, whether localized disruption to cell adhesion junctions within domains of viral infection in embryonic chick and postnatal rat hearts results in (I) disturbances to normal differentiation of gap unction distribution and (ii) changes in conduction of AP in intact tissues and/or the emergence of ECG abnormalities comparable to those observed in cardiac pathologies also characterized by discrete foci of electromechanical dysfunction (eg, infarct border zones in ischemic heart disease and regions of myofiber disarray in hypertrophic cardiomyopathy).